This invention relates to liquid electrophotographic reproduction machines, and more particularly to a method of making a microporous surface blotter roll for removing carrier liquid from toner dispersant used in such machines to form toner images.
A liquid electrostatographic reproduction machine employs an imaging member that is exposed to an image to be printed. Exposure of the imaging member records an electrostatic latent image on it corresponding to informational areas contained within the image to be printed.
The latent image is developed by bringing a developer material into contact therewith. The developed image recorded on the photoconductive member is conditioned and then transferred to a support substrate such as paper, either directly or via an intermediate transport member. The developed image on the support substrate is subsequently subjected to heat and/or pressure in order to permanently fuse it to the substrate.
Liquid developer typically contains about 2 percent by weight of fine solid particulate toner material that is dispersed in a carrier liquid, such as a hydrocarbon. The developed image on the imaging member or photoreceptor ordinarily contains about 12 weight percent of particulate toner material or particles in the hydrocarbon carrier liquid. Conditioning such an image therefore includes increasing the percent solids of the image by removing carrier liquid from the image while preventing the solid toner particles from leaving the image, and of electrostatically compressing or compacting the toner particles in order to physically stabilize the image, and produce a clear, high resolution image.
Such conditioning must however be achieved without disturbing the toner image, and in such a manner to prevent toner particles from entering the carrier liquid removal device. In addition, the carrier liquid removal device must also remain clean and free of toner particles so as to prevent it from thereafter contaminating a subsequent image with embedded toner particles.
Various techniques and devices including blotter rolls or rollers have been devised for conditioning the liquid developer image by removing carrier liquid from the image as discussed above. Such blotter rolls may include a vacuum removal system or an electrical bias applied thereto in order to assist the removal process. The following references may be relevant to various aspects of the present invention.
U.S. Pat. No. 4,286,039 issued Aug. 25, 1981, discloses an image forming apparatus comprising a deformable polyurethane roller, which may be a squeegee roller or blotting roller which is biased by a potential having a sign the same as the sign of the charged toner particles in a liquid developer. The bias on the polyurethane roller is such that it prevents streaking, smearing, tailing or distortion of the developed electrostatic image and removes much of the carrier liquid of the liquid developer from the surface of the photoconductor.
U.S. Pat. No. 4,985,733 issued Jan. 15, 1991, to Kurotori et. al. discloses a liquid toner copying machine including a non-thermal image conditioning apparatus comprising an elastic blotter roll and an elastic backup roller for bringing a liquid toner image carrying sheet into contact with the blotter roll.
U.S. Pat. No. 5,136,334 issued Aug. 4, 1992, to Camis et. al. discloses a liquid toner image conditioning apparatus including a heated inner core connected to a source of AC or DC bias, and having a smooth outer surface made of a soft elastomeric material.
U.S. Pat. No. 5,332,642, issued Jul. 26, 1994, having a common assignee as the present application, discloses a porous roller for increasing the solids content of an image formed from a liquid developer. The liquid dispersant absorbed through the roller is vacuumed out through a central cavity of the roller. The roller core and/or the absorbent material formed around the core may be biased with the same charge as the toner so that the toner is repelled from the roller while the dispersant is absorbed.
U.S. Pat. No. 5,424,813, issued Jun. 13, 1995, to Schlueter et. al., and having a common assignee as the present application discloses a roller comprising an absorption material and a covering, which are adapted to absorb carrier liquid from a liquid developer image. The covering has a smooth surface with a plurality of perforations, to permit carrier liquid to pass through to the absorption material at an increased rate, while maintaining a covering having a smooth surface which is substantially impervious to toner particles yet pervious to carrier liquid so as to inhibit toner particles from departing the image.
Although some of the above example references suggest or disclose particular structures for a blotter roll, it has been found that much difficulty is encountered in fabricating a blotter roll that has a microporous surface, controlled, uniform size open cells, and an efficient liquid transport interface between the microporous surface layer and an underlying absorbent larger cell open cell layer.